This invention pertains to pipe string components used to exercise flow controls primarily, but not in a limiting sense, for use in wells during completion work. The invention reduces surge pressure down hole and surge pressure induced flow from the top of pipe strings being run into wells.
During the completion of petroleum related wells several lengths of casing are run into the well while it is filled with mud or well produced fluids. While the rather long strings of pipe are moving into the well, the fluids fill the newly lowered pipe.
If casing or liner pipe strings are moving axially along the well bore the resulting pressure differentials along the bore can be destructive. The casing acts as a pump plunger and may be driven by several hundred tons of steel pipe. Serious formation damage can result. To prevent formation damage, the pipe string is moved slowly to allow fluid to flow around and through the pipe string to reduce the pressure effects. Moving slowly takes more time for well completion and time is costly and may well invite hazards to property and personnel.
When the formation damage risk is avoided, there are other problems that arise from moving pipe into wells. There is some flow resistance and the fluid is still flowing into the moving pipe when the top end of the pipe string is stopped just above the rig floor to add a new pipe section to the string. Flowing fluid, in a long pipe, is not easily stopped and it flows out the top of the pipe, usually before downward movement of the string is completed. The well fluid flows over personnel, rig machinery, and rig floor. The fluid adds to personnel risks, is slippery, and generally unpleasant.
Casing or liner that does not extend to the surface when installed is put in place by a working string that is, finally, disconnected from the placed installation string. The working and installation strings are connected by an adapter. The working string has a small bore compared with the flow area of the annulus between the working string and the well bore. The flow area of the annulus is needed to reduce surge pressure below the installation string. Fluids below the casing are less likely to build up destructive pressure that damages formation, or flow over the top end of the working string if they can be vented into the well annulus above the pipe string being installed.
The adapters have been constructed such that the upwardly moving fluid can flow in both the annulus and the pipe string bore. Further adaptation has made it possible to pump fluid down the string without losing it to the annulus at the adapter. When installing pipe strings in wells it is often necessary to circulate to ease past tight spots and to blow out bridges.
To date, maximizing protection of the formation, and optimizing installation speed has not eliminated the overflow of fluid at the top of the working string. The prospect of using a flow resistor in the working string bore is discouraged because a wide open pipe bore is needed for some well completing operations, including the running of cement. There is a need to provide means to allow free flow downwardly in the working string, but to restrict upwardly moving fluid so that the annulus fluid level, drained at the surface, will be above the level of fluid rising in the bore of the working string. Then, fluid will not flow over the top of the working string.
The apparatus of the invention will usually be installed between a working pipe string, usually a drill string, and an installation pipe string such as casing or a casing liner. The arrangement permits upward flow of fluid in both the bore and annulus of the working string. Flow up the working string bore is resisted so that flow will not rise in the working string and spill over the top. The need to pump fluid down working and the installation strings to cope with problems, and proceed with completion is satisfied by a controllable secondary up-flow route. Fluid from the bore of the installation string, with up-flow blocked by a temporary blockage in the string bore, passes through a closable pipe wall opening to the working string annulus and is admitted back to the working string bore through a check valve that resists inward flow and prevents out flow. Surge pressure is reduced without allowing fluid to spill over the top of the working string.
To close the secondary flow route and open the temporarily blocked pipe string bore, a pressure sensitive blow-out element is carried by a piston that closes the secondary flow route in response to forced down flow in the working string bore. The secondary flow route is closed before the down-flow in the working string bore blows the obstruction out of the piston. The obstruction may be a burst disc-or an elastomer ball that will blow through an undersize hole at a selected pressure.
In the event it becomes necessary to pump fluid down the bore of the working string before the installation string is finally in place, another similar apparatus can be installed in the working string as it""s assembly proceeds. The resisted upward flow in the newly installed adapter will prevent overflow of the top of the pipe string.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.